249 research outputs found
Multi-band spectroscopy of inhomogeneous Mott-insulator states of ultracold bosons
In this work, we use inelastic scattering of light to study the response of
inhomogeneous Mott-insulator gases to external excitations. The experimental
setup and procedure to probe the atomic Mott states are presented in detail. We
discuss the link between the energy absorbed by the gases and accessible
experimental parameters as well as the linearity of the response to the
scattering of light. We investigate the excitations of the system in multiple
energy bands and a band-mapping technique allows us to identify band and
momentum of the excited atoms. In addition the momentum distribution in the
Mott states which is spread over the entire first Brillouin zone enables us to
reconstruct the dispersion relation in the high energy bands using a single
Bragg excitation with a fixed momentum transfer.Comment: 19 pages, 7 figure
Counterflow of spontaneous mass currents in trapped spin-orbit coupled Fermi gases
We use the Bogoliubov-de Gennes formalism and study the ground-state phases
of trapped spin-orbit coupled Fermi gases in two dimensions. Our main finding
is that the presence of a symmetric (Rashba type) spin-orbit coupling
spontaneously induces counterflowing mass currents in the vicinity of the trap
edge, i.e. and particles circulate in opposite
directions with equal speed. These currents flow even in noninteracting
systems, but their strength decreases toward the molecular BEC limit, which can
be achieved either by increasing the spin-orbit coupling or the interaction
strength. These currents are also quite robust against the effects of
asymmetric spin-orbit couplings in and directions, gradually reducing
to zero as the spin-orbit coupling becomes one dimensional. We compare our
results with those of chiral p-wave superfluids/superconductors.Comment: 6 pages with 4 figures; to appear in PR
Momentum-resolved study of an array of 1D strongly phase-fluctuating Bose gases
We investigate the coherence properties of an array of one-dimensional Bose
gases with short-scale phase fluctuations. The momentum distribution is
measured using Bragg spectroscopy and an effective coherence length of the
whole ensemble is defined. In addition, we propose and demonstrate that
time-of-flight absorption imaging can be used as a simple probe to directly
measure the coherence-length of 1D gases in the regime where phase-fluctuations
are strong. This method is suitable for future studies such as investigating
the effect of disorder on the phase coherence.Comment: 4 pages, 4 figure
Double species condensate with tunable interspecies interactions
We produce Bose-Einstein condensates of two different species, Rb and
K, in an optical dipole trap in proximity of interspecies Feshbach
resonances. We discover and characterize two Feshbach resonances, located
around 35 and 79 G, by observing the three-body losses and the elastic
cross-section. The narrower resonance is exploited to create a double species
condensate with tunable interactions. Our system opens the way to the
exploration of double species Mott insulators and, more in general, of the
quantum phase diagram of the two species Bose-Hubbard model.Comment: 4 pages, 4 figure
Intense slow beams of bosonic potassium isotopes
We report on an experimental realization of a two-dimensional magneto-optical
trap (2D-MOT) that allows the generation of cold atomic beams of 39K and 41K
bosonic potassium isotopes. The high measured fluxes up to 1.0x10^11 atoms/s
and low atomic velocities around 33 m/s are well suited for a fast and reliable
3D-MOT loading, a basilar feature for new generation experiments on
Bose-Einstein condensation of dilute atomic samples. We also present a simple
multilevel theoretical model for the calculation of the light-induced force
acting on an atom moving in a MOT. The model gives a good agreement between
predicted and measured flux and velocity values for our 2D-MOT.Comment: Updated references, 1 figure added, 10 pages, 9 figure
Collisional properties of sympathetically cooled K
We report the experimental evidence of the sympathetic cooling of K
with Rb down to 1 K, obtained in a novel tight confining magnetic
trap. This allowed us to perform the first direct measurement of the elastic
cross section of K below 50 K. The result obtained for the triplet
scattering length, Bohr radii, agrees with previous results
derived from photoassociation spectra and from Feshbach spectroscopy of
K.Comment: 7 pages, 4 figures, submitted to Phys. Rev.
Coherent Manipulation of Orbital Feshbach Molecules of Two-Electron Atoms
Ultracold molecules have experienced increasing attention in recent years.
Compared to ultracold atoms, they possess several unique properties that make
them perfect candidates for the implementation of new quantum-technological
applications in several fields, from quantum simulation to quantum sensing and
metrology. In particular, ultracold molecules of two-electron atoms (such as
strontium or ytterbium) also inherit the peculiar properties of these atomic
species, above all the possibility to access metastable electronic states via
direct excitation on optical clock transitions with ultimate sensitivity and
accuracy. In this paper we report on the production and coherent manipulation
of molecular bound states of two fermionic Yb atoms in different
electronic (orbital) states S and P in proximity of a
scattering resonance involving atoms in different spin and electronic states,
called orbital Feshbach resonance. We demonstrate that orbital molecules can be
coherently photoassociated starting from a gas of ground-state atoms in a
three-dimensional optical lattices by observing several photoassociation and
photodissociation cycles. We also show the possibility to coherently control
the molecular internal state by using Raman-assisted transfer to swap the
nuclear spin of one of the atoms forming the molecule, thus demonstrating a
powerful manipulation and detection tool of these molecular bound states.
Finally, by exploiting this peculiar detection technique we provide first
information on the lifetime of the molecular states in a many-body setting,
paving the way towards future investigations of strongly interacting Fermi
gases in a still unexplored regime.Comment: 11 pages, 8 figure
A strongly interacting gas of two-electron fermions at an orbital Feshbach resonance
We report on the experimental observation of a strongly interacting gas of
ultracold two-electron fermions with orbital degree of freedom and magnetically
tunable interactions. This realization has been enabled by the demonstration of
a novel kind of Feshbach resonance occurring in the scattering of two 173Yb
atoms in different nuclear and electronic states. The strongly interacting
regime at resonance is evidenced by the observation of anisotropic hydrodynamic
expansion of the two-orbital Fermi gas. These results pave the way towards the
realization of new quantum states of matter with strongly correlated fermions
with orbital degree of freedom.Comment: 5 pages, 4 figure
Superradiant light scattering from a moving Bose-Einstein condensate
We investigate the interaction of a moving BEC with a far detuned laser beam.
Superradiant Rayleigh scattering arises from the spontaneous formation of a
matter-wave grating due to the interference of two wavepackets with different
momenta. The system is described by the CARL-BEC model which is a
generalization of the Gross-Pitaevskii model to include the self-consistent
evolution of the scattered field. The experiment gives evidence of a damping of
the matter-wave grating which depends on the initial velocity of the
condensate. We describe this damping in terms of a phase-diffusion decoherence
process, in good agreement with the experimental results
Sensitive measurement of forces at micron scale using Bloch oscillations of ultracold atoms
We show that Bloch oscillations of ultracold fermionic atoms in the periodic
potential of an optical lattice can be used for a sensitive measurement of
forces at the micrometer length scale, e.g. in the vicinity of dielectric
surface. In particular, the proposed approach allows to perform a local and
direct measurement of the Casimir-Polder force which is, for realistic
experimental parameters, as large as 10^-4 gravity
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